An electromechanical actuator 100 (FIG. 1) for a valve 110 comprises mechanical means, such as springs 102 and 104, and electromagnetic means, such as electromagnets 106 and 108, for controlling the position of the valve 110 by means of electric signals.
The rod of the valve 110 is applied for this purpose against the rod 112 of a magnetic plate 114 located between the two electromagnets 106 and 108.
When current flows in the coil 109 of the electromagnet 108, the latter is activated and generates a magnetic field attracting the plate 114, which comes into contact with it.
The simultaneous displacement of the rod 112 enables the spring 102 to bring the valve 110 into the closed position, the head of the valve 110 coming into contact with the seat 111 and preventing the exchange of gas between the interior and the exterior of the cylinder 117.
Analogously (not shown), when a current flows in the coil 107 of the electromagnet 106, the electromagnet 108 being deactivated, and it is activated and it attracts the plate 114, which comes into contact with it and displaces the rod 112 by means of the spring 104 in such a way that this rod 112 acts on the valve 110 and brings the latter into the open position, the head of the valve being moved away from its seat 111 to permit, for example, the admission or the injection of gas into the cylinder 117.
Thus, the valve 110 alternates between the open and closed positions, the so-called switched positions, with transient displacements between these two positions. The open or closed state of a valve will hereinafter be called the “switched state.”
The actuator 100 may also be equipped with a magnet 118, which is located in the electromagnet 108, and with a magnet 116, which is located in the electromagnet 106, the magnets being intended to reduce the energy necessary for maintaining the plate 114 in a switched position.
Each magnet is located for this purpose between two subelements of the electromagnet with which it is associated in such a way that its magnetic field, possibly combined with the field generated by the electromagnet, supports the maintenance of the valve 110 in the open or closed position. For example, the magnet 116 is located between two subelements 106a and 106b.
Due to the action of the magnet on the magnetic plate, such an electromagnet 106 or 108, called an electromagnet with magnet or polarized electromagnet, requires considerably less energy for controlling a valve, as the maintenance of a valve in a switched position represents a considerable energy consumption for the actuator.
The present invention results from the observation that the actuator 100 has numerous drawbacks.
In fact, this actuator requires the use of two distinct subelements 106a and 106b to form an electromagnet 106. Operations peculiar to the manufacture and the stocking of each of these subelements are therefore necessary, which increases the complexity and the manufacturing costs of the actuator.
Moreover, the operation required for assembling these subelements 106a and 106b with the magnet 116 increases the cost and the complexity of the manufacture of the actuator, and there is a risk during this assembly that the subelements 106a and 106b and/or the magnet 116 may be assembled incorrectly or that they will be damaged, which would reduce the performance of the electromagnet.
A new drawback is the difficulty of a possible replacement of a magnet 116 or 118. In fact, it is necessary to disassemble the electromagnet unit 106 to replace a defective magnet 116.
Another drawback is the considerable size of the actuator 100, which is due especially to the fact that its height h is dictated by the cross section Sa of the magnets 116 and 118. This cross section Sa is, in fact, considerable in order to obtain a high magnetic flux from these magnets.
In addition, such an actuator has a considerable leakage due to the dispersion of the magnetic flux in the air gaps.
The actuator 100 also requires the use of a magnetic plate 114 of a large mass due especially to its considerable cross section Sp. In fact, this cross section is, in general, equal to the cross section Se of the branches of the electromagnet to achieve optimal functioning of the actuator, as the branches of the support of the electromagnet and the plate form a magnetic circuit of constant cross section.
However, the use of a plate 114 of a considerable cross section and consequently of a large mass has numerous drawbacks, which were described above.
First, the actuator 100 requires springs of high rigidity to displace the considerable mass of the plate. Consequently, the sensitivity of the control exerted by the electromagnets on the plate by means of the current flowing in the coils is reduced, while the consumption required by the electromagnet for controlling the plate is increased.
The use of springs of increased rigidity causes, as a corollary, the latter to form an oscillating device with the mobile elements of the actuator 100, which said device is characterized by a switching time that is fixed more or less by the rigidity k102 and k104 of the springs 102 and 104 and by the mass md of the elements being displaced (plate 114, rod 112, mobile mass of the springs 102 and 104, and valve 110).
Second, the energy lost, e.g., in the form of the operating noise of the actuator due to the impact of the plate on the electromagnet is generally increased by an increase in the mass of the plate. Such an increase in the energy loss causes a lower energy efficiency of the actuator.